Optical transport networks, such as synchronous optical networks (SONET) or synchronous digital hierarchy (SDH) networks, are composed of a set of optical network elements connected by optical fiber links and are able to provide the functionality of transport, multiplexing, switching, management, supervision and survivability of optical channels carrying client signals. Optical network elements include optical cross-connects (OCXs) for rerouting an optical signal from an input port to an output port, reconfigurable optical add-drop multiplexers (ROADMs) for the adding and dropping of wavelengths, transponders, routers, and various optical-to0electrical (O/E) and electrical-to-optical (E/O) converters.
Optical transport networks employ a number of path protection and link protection mechanisms to mitigate data losses when a communications failure occurs between two nodes of the network. In both path protection and link protection, backup resources are identified during connection setup. In path protection, when a failure occurs between two nodes, the source and destination nodes dynamically determine an alternate path using transport layer communications in order to restore the connection (a process called “restoration”). In link protection, when a failure occurs between two nodes, the adjacent nodes dynamically determine an alternate link using physical layer communications in order to restore the connection, while the source and destination nodes remain unaware of the failure. To prevent contention between the two mechanisms, current networks usually employ either path protection or link protection with the alternate mechanism disabled. It would be desirable to operate the optical transport network with both mechanisms enabled.